Recognizing Mediastinitis

Nanette Lavoie-Vaughan, ARNP-C, MSN
Along with stroke and sudden death, mediastinitis is one of the most devastating
complications of cardiac surgery.

Nurse Smith, RN, had been assigned to a 62-year-old patient 10 days after her
coronary artery bypass graft (CABG). The history included diabetes, COPD,
hypertension, and mild obesity. During report, Smith learned a yellow discharge was
present when the incisional dressing was changed that morning. The patient also had
a low-grade fever and had been complaining of substernal pain on movement.

Smith’s initial assessment revealed the patient was mildly dyspnic, restless,
clutching her chest, and complaining of midline chest pressure at the incision site
when she moved. When Smith positioned the patient to assess her lungs, a “popping
sound” was heard in the patient’s chest wall. Smith immediately called the physician,
who ordered a chest x-ray, chest CT, CBC, and blood and wound cultures.

As Smith suspected, the diagnosis was acute mediastinitis, and the patient was
started on antibiotics immediately.

Dangerous and on the rise

Acute mediastinitis is an infectious process involving all or part of the mediastinum,
the cavity between the lungs, which contains many important structures. (See
illustration.) It is most common in patients recovering from cardiac surgery, but it can
also occur as a result of an esophageal tear from excessive vomiting, trauma, or
instrumentation. Chronic mediastinitis may arise from tuberculosis, histoplasmosis,
fungal infections, cancer, and sarcoidosis.

Along with stroke and sudden death, it’s one of the most devastating complications of
cardiac surgery. It occurs, on average, in 1% to 2% of surgical patients, but it’s now
on the rise because of concomitant factors, such as heart transplants, obesity, and
diabetes.1 COPD, smoking, renal failure, and advanced age are also implicated.

Certain procedures and conditions greatly increase the risk for postoperative
mediastinitis, including the use of bilateral internal mammary grafts, emergency
surgery, cardiopulmonary resuscitation, prolonged bypass and operating time,
postoperative shock, obesity greater than 20% of ideal body weight, re-exploration
following initial surgery, and sternal wound dehiscence. Surgical technique factors
such as excessive use of electrocautery and bone wax, paramedian sternotomy, and
pacing wires also increase the incidence.1,3,4

The causative organisms are Staphylococcus aureus and Staphylococcus epidermis
in 70% to 80% of infected patients. Mixed gram-negative and gram-positive infections
cause 40% of cases. The overall rise of methicillin-resistant Staphylococcus aureus
(MRSA) infections has also had an impact on the prevalence of this condition and
accounts for 25% to 30% of all cases of acute mediastinitis.1

Even though the incidence is low, the sequelae of reoperation, prolonged ventilation,
additional time in the ICU, and increased need for follow-up assistance after
discharge compound the cost of recovery and increase the risk of death. Mortality
rates are between 19% and 47%, and comorbidity is as high as 67%.2

Acute mediastinitis is divided into types based on the time frame following the
surgery and accompanying risk factors. (See “Acute Mediastinitis” sidebar.)

Be alert for acute mediastinitis

Nurses need a high index of suspicion to detect mediastinitis. Assessing the wound
provides clues to early signs of trouble.

There are several key points for early detection of acute mediastinitis in postoperative
wounds. For wounds closed by primary intention, observe the edges of the wound.
Suspect wounds are not well approximated and have a decreased inflammatory
response, drainage that continues more than two days postoperatively, and no
healing ridge present by the ninth day post surgery.

In wounds closed by secondary intention, observe for granulation tissue that remains
pale, a wound that is excessively dry or moist, drainage with an abnormal odor,
sloughing or necrotic tissue, and tunneling or undermining of tissue surrounding the
wound.

In a patient who has developed mediastinitis, symptoms include complaints of
increased pain in the mid-sternal area associated with a clicking or popping sound,
indicating an unstable chest wall. Other symptoms may be chills, malaise, and
tenderness of the chest wall.

The presence of deep sternal wounds, which typically occur seven to 10 days after
surgery, is suspicious for acute mediastinitis. The patient may be afebrile. Red flags
are increased drainage and an unstable chest wall. Chest auscultation often reveals a
crunching sound (Hamman’s sign) over the precordium during systole. Leukocytosis
may be absent. A chest x-ray confirms a shift in sternal wires and a CT scan may
show sternal separation, soft tissue inflammation, and the presence of fluid. Needle
aspiration identifies the causative organism.

Types of therapy

Once a diagnosis is made, therapy is initiated to prevent or treat septicemia, remove
all infected and necrotic tissue, provide wound protection and coverage, and
reestablish sternal stability.

A pectoralis major myocutaneous skin flap can provide primary soft tissue coverage.
If the wound is too large or not suited for a flap, omental packing in the open cavity
with polyurethane foam will protect the wound and absorb excess drainage. Sternal
rewiring has proven effective for treating patients with early, deep sternal infection and
dehiscence.

Antibiotic treatments are organism-specific and determined on a case-by-case basis.
Because of the increased incidence of MRSA, a large percentage of patients are
treated with vancomycin for four to six weeks and sometimes for several months.

Vacuum-assisted closure has been used successfully as a primary therapy in
patients with advanced mediastinitis (types 4 and 5) and can hasten wound
debridement before flap closure. This negative-pressure pumping device draws
drainage, bacteria, and excess blood from the wound, which allows a cleaner wound
bed. The suction also stimulates surrounding blood vessels and cells to grow,
resulting in better, faster healing.5

Untreated, mediastinitis can cause osteomyelitis, pericarditits, pneumonia,
septicemia, and permanent damage to organs and vessels in the mediastinum.

Postoperative wound care

Infection control is imperative and meticulous pre- and postoperative skin care is
needed to prevent contamination of the incision. (See “Infection Control Intervention
for Cardiac Patients” sidebar.)

To prevent infection and tissue damage, nurses should —

  • Wash area surrounding wound with soap and water. Avoid friction if tissue is
    friable.
  • Irrigate wound using a 35-ml syringe with an 18-gauge flexible IV catheter (to
    provide high pressure). Use 100 ml to 150 ml of irrigating solution to remove
    contaminants.
  • Apply topical enzymes (when prescribed), following directions carefully. Avoid
    use of providone iodine, which deactivates enzymes.

Nurses are on the front lines when it comes to making a difference in outcomes. By
knowing the risk factors, signs, and symptoms for acute mediastinitis, nurses can
intervene early enough to prevent significant tissue damage and even death.
Nanette Lavoie-Vaughan, M.S.N., APN
ARTICLE LINKS:

Infection Control Intervention
Acute Mediastinitis
Article References